CXCR4 and cancer: At the same time, a chronic hypoxia-induced increase in CXCR4 expression stimulates the proliferation of cancer cells [256,275] and causes their migration and invasion [244,246,248,249,255,256,257,275], especially in combination with the chronic hypoxia-induced increase in CXCL12 expression in tumor cells [167,223,228].